Rf-GDOES analysis of composite metal/ceramic electroplated coatings with nano- to microceramic particles' size: Issues in plasma sputtering of Ni/micro-SiC coatings

Ni matrix composite coatings reinforced with nano- and microceramic particles were analyzed by radio frequency glow discharge optical emission spectrometry (Rf-GDOES). An interesting phenomenon related to the sputtering and excitation modes of this technique was observed. During plasma sputtering with Rf-GDOES, the micro-SiC particles were detached from metal matrix and did not contribute to the analytical signals. The same was not found in composite coatings containing nanoceramic particles. This anomalous behavior was confirmed by atomic force microscopy (AFM) investigation and scanning electron microscope (SEM) observations into Rf-GDOES craters that showed the presence of residual non-sputtered microparticles. Various attempts were done in order to minimize this problem, mainly by varying the analysis parameters of the used instrumentation, but without any relevant success. Some suggestions were then proposed for explaining the observed phenomenon, moreover possible solutions (e.g. by using a strong magnetic field or changing plasma gas to be more energetic) are discussed.